A fuel cell differs from a battery in that it is a thermodynamically open system where the fuel source reactant is continuously supplied from an external source. A microbial fuel cell uses the metabolic process of microbes (such as bacteria, for example) from the surrounding environment to convert chemical energy into electrical energy. More specifically, electrical charges are generated and expelled during the metabolic process of bacteria, which converts biological organic soil content, such as acetates, fatty acids, and aromatics, into by-products of carbon dioxide and positive hydrogen ions. Compared to traditional fuel cells, microbial fuel cells can be more flexible to operate and less expensive to construct.
For a microbial fuel cell to function more effectively, the generated charges must effectively transfer from the bacteria to the anode for the microbial fuel cell. Once this occurs, the charges can travel across and through the anode to either serve as an electric energy source to instantaneously power load electronics, or to charge storage devices such as batteries, capacitors, super capacitors and similar components. Energy (electrical charges, or electrons) that is not dissipated in the load electronics can continue to flow to the cathode, to chemically react with oxygen and positive ions and thereby create thermal energy and chemical by-products.
Graphite materials are predominantly used as fuel cell electrodes in sediment microbial fuel cells because they are inexpensive, electrically conductive, inert, and corrosion resistant. But the power performance of fuel cells comprised of these materials can be hindered because of a graphite system's inability to operate effectively in diverse operation conditions where pH, temperature, salinity, availability of organic matter, and buildup of oxidation products are issues. For this reason, other carbon-based materials such as nanotubes, rods, fibers, whiskers, sponges, fabric, expandable graphite, carbon black, graphene, and fullerenes are often used as material components for fuel cell electrodes in addition to graphite. Electrodes containing one or more of these types of carbon-based materials can show improved electrical conductivity, structural stability, and thermal stability when formulated and processed in an optimized manner when compared to electrodes that are made of pure graphite. These improved material properties can persist even after prolonged exposure to harsh and extreme operating conditions.
Studies in the prior art have also shown that in addition to durability, fuel cell performance can be enhanced by modifying the electrode material formulation. Sediment microbial fuel cells that are deployed in sandy and marine environments have been observed to provide power densities of 1.4-70 milliWatts per square meter (mW/m2), which can be enough energy to operate low-powered sensors and devices. The prior art further discloses that anaerobic bacteria can drive the energy production process of sediment microbial fuel cells by metabolizing biological organic matter from the surrounding environment. Sediment microbial fuel cell anodes have been created from carbon cloth pouches filled with chitin or cellulose, which are insoluble biological compounds. The presence of biomolecules such as chitin or cellulose increased the maximum power density of the sediment fuel cells to 176-272 mW/m2. The power density was also observed to increase as the particle size of chitin decreased. An increase in fuel cell operation time (up to 33 days) was also observed with the presence of chitin and cellulose. Thus, the prior art indicates that the presence of chitin and cellulose introduced an insoluble natural food source that quickly attracted anaerobic bacteria to the sediment fuel cell system, which is needed to drive and sustain the energy production process. As a result, the power performance of carbon-based sediment microbial fuel cells can be further enhanced with the presence of biological compounds.
In view of the above, it is an object of the present invention to provide a microbial fuel cell and methods for manufacture that provide a surface graft matrix that binds biologics (biomolecules and biological agents) to the electrode of a microbial fuel cell. Another object of the present invention is to provide a microbial fuel cell and methods for manufacture that provides an enhanced microbial environment for attracting anaerobic bacteria to metabolize biomolecules. Yet another object of the present invention is to provide a microbial fuel cell and methods for manufacture, which integrates a surface graft matrix that binds biological agents to the fuel cell to yield increased power output relative to similar-sized fuel cells. Still another object of the present invention is to provide a microbial fuel cell and methods for manufacture that maintains consistent power generation capacity, even in austere undersea environments. Another object of the present invention is to provide a microbial fuel cell and methods for manufacture that can be easily manufactured in a cost-effective manner.